These accidentals are in the same place of the notes that they will change, in other words, they change all the notes in that specific line or space. Let’s say that you received a sheet music that has a key signature in B flat (the line that corresponds to B has a flat sign). This means that you have to decrease a semitone of all “B” notes that will appear ahead, like the example below:
Example of a Key Signature with an accidental
We highlighted in red the B notes in the Treble and Bass Clefs above to give you emphasis. Notice that in these lines there is a “b” indicating “flat” in the Key Signatures. When you play, you have to keep in mind the Key Signature command.
How to discover the tonality just looking at the Key Signature?
The Key Signatures also help to reveal the tonality of a song. For example, think about G major scale, this has just one accidental (F#), right? So, a sheet music that has F# in its Key Signature indicates that the song is in G major. Check other examples:
Observation: Notice that the tonalities can also be minor. In this case, instead of G major, for example, we could have E minor (its relative minor). We cannot conclude this immediately just looking at the Key Signature; it will depend on the context.
Tips to read a Key Signature in practice
What we showed you may seem useless if you don’t know the accidentals in all the scales by heart. Well, let’s show you some ‘ins and outs’ to make things easier: when we have a Key Signature with sharps, it doesn’t matter how many are they, you will discover the tonality just looking at the last sharp (observation: the order is from left to right). In the example below, this is the last sharp:
The tonality of this song will be one degree above the last sharp. In the example above, the last sharp was in C, therefore, the tonality is D major.
Observation: one degree is the next line or space.
If you want to know the relative minor tonality, it’s just to take one degree below this last sharp. In the same previous example, one degree below of C is B, therefore, the tonality would be B minor.
Observation: If the note that you found has also an accidental in the Key Signature, you need to apply this accidental to the tonality, for example, in the Key Signature below, the last sharp is in E, what leads us to conclude that the tonality is F major. But F already has a sharp in the Key Signature, so the tonality is F sharp and not F!
Key Signature with Flat Accidentals
For Key Signatures with flat the rule is even easier. The penultimate flat will indicate the major tone (followed by the flat alteration) and two degrees of this tone you will find the minor tone:
Observation: There are just two exceptions to these rules that we gave you. The first is the Key Signature with just one flat (Bb), which will indicate the tonality of F major or D minor. And the second is the empty Key Signature, which will indicate the tonality of C major or A minor. You need to memorize these two exceptions!
If you observe well the Key Signatures that were shown here, you will see that all the accidentals are registered following the same logic: the sharps appear according to the sequence of circle of fifths, starting in F. And the flats appear following the circle of fourths, starting in B. In practice, knowing this is only relevant for those who will write sheet music. Try to memorize the details about Key Signature that will be important for you purpose as a musician, whether writing, reading or both.
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